Sleepless in Las Vegas (Harlequin Superromance)

Ranked #1 by book review site ME, MY SHELF AND I in three categories: Most Beautifully Written Book in 2013, Best New Genre (for reviewer), and Most Surprising Book of 2013!
Book Blurb
This investigation is getting very personal 

P.I.-in-training Valerie LeRoy is dying to get into the field. So when a client asks her to spy on someone, the thrill of her own case is too tempting to refuse. Instead of a cheating fiancée, however, Val's actually checking out P.I. Drake Morgan! Worse, she ends up working with the guy. 

Their differing opinions on techniques--and the instant attraction--make the sparks fly. It's almost impossible to focus on their arson investigation. As the hunt for the truth intensifies and their passion rivals the triple-digit temperature, she and Drake learn why Las Vegas is the city that never sleeps....